Protective means for electric circuits



i Nov. QQ@ Q W, MULLER 2,179,342

l PROTECTIVE MEANs FCR ELECTRIC CIRCUITS' Filed Dec. s, 1955 zsneets-shet 1 Inventor# Nav. 7, 193gJ w, MULLER 2,79,342

ERTLEETIWE FOB ELETBIC CIRCUITS l-is Attorney.

I Patented Nov. 7, 1939 2,179,342 PnoTEoTlvE MEANS Fon ELECTRIC omcUrTs ('llstav W. Mller, Berlin-Charlottenburg, Germany, assignor to General Electric Company, a corporation of New York Application December' 3, 1935, Serial No. 52,711 In Germany December 20, 1934 8 Claims.

'Ihe present invention relates to protective means for electric circuits and particularly to an improved construction for a fuse device suitable for interruption of high tension circuits.

Heretoforefuses suitable for high tension duty have been constructed with the `fusible element arranged in a tube iilled with arc quenching liquid and with provision made for the drawing apart of the fuse terminals or` contacts upon fusing of the fuse element to eiect thereby extension of the arc path. The employment of a restricted chamber for the quenching of the arc has been another expedient. However, when such arrangements have been employed in the past, there has been encountered among others the disadvantage that the arc has been drawn out of the chamber when the contacts were sepav rated, so that the quenching action has taken place only partially in the chamber with the greater part of such action taking place in the tube lled with liquid.

The present invention has for ne of its objects the provision of improvements for increasing the eiectivenes and safety of operation of fuses of the liquid-iilled type having means for effecting separation of the fuse terminals upon fuse operation.

A further 'and important object of the present invention is the provision of an improved fuse construction wherein the pressure resistant arc quenching chamber is extended coincidently with the separation of the fuse terminals so that the lengthened arc is madeto remain in the pressure resistant chamber to be quenched, thereby avoiding the disadvantages attendant upon the use of the previously known constructions outlined above. f

Another object of the invention is the provision of a. fuse construction suitable for employment in the practice of the invention of my application Serial No. 200,956, filed April 8, 1938, which said application is a division oi the present application and is assigned to the same assignee as the present invention.

Other objects and the details of that which I consider to be novel and my present invention will be apparent from the following description and the claims 'appended thereto, taken in conjunction with the accompanying drawings in which Fig. 1 is a longitudinal section through a fuse device constructed in accordance with the present invention showing the parts of the device in the positions they assume when the fusible element is intact,

(Cl. 20G-117) Fig. 2 shows the parts of the fuse device in the positions they assume aiter rupture of the :fusible element,

Fig. 3 is a partially diagrammatic longitudinal sectional view of a modified form of fuse device embodying the invention,

Fig. 4 is a view, partially in cross section, oi a further modiiication of the fuse device,

Fig. 5 illustrates diagrammatically a protective arrangement for an electric circuit incorporating a fuse device of the type illustrated in Fig. 4, and

Fig. 6 is a diagrammatic illustration of a protective arrangement incorporating a fuse device of the type illustrated in Fig. 4 and designed for the isolation of electric conversion apparatus.

Referring to Figs. 1 and 2 of the drawings, I Il Ydenotes a hollow tubular casing of suitable insulation material in which is disposed a body of oil or other arc quenching liquid II. 'I'he upper and lower ends of the easing are provided with metallic end caps I2 and I3 respectively. In the upper cap I2 is mounted a connection terminal or contact I4 through which passes the supporting shank I5 of a fusible element I6. The lower end of the fusible element is attached to a connection terminal or contact I'l in any suitable manner as, for example, by means of a screw cap such as that indicated at I8. 'I'he lower end oi' the terminal i'l is connected by means of the exible extension conductor I9 to the lower end cap I3.

'End cap I2 is provided with an inwardly extending iiange 20 having an outer screw threaded portion upon which is mounted a tubular casing 2| of suitable insulation material which extends downwardly in and substantially coaxially of the outer casing I0 to a point considerably below the liquid level line. A third tubular member or casing 22 of insulation material is disposed within the casing I0 and is shown in Fig. 1 as being telescoped within the tube 2|. The inner tube 22 is arranged to slide Within the casing I0 into and out of the tube 2l -and'is provided with an outwardly extending shoulder 23 which serves to guide the tube in the casing I0. The tube 22 is also formed with an inwardly projecting portion 24 and is provided with an inwardly projecting annular metallic ring 25, which projections aid, when the parts of the fuse device are in the position shown in Fig. 1, in maintaining the tube 22 substantially coaxial with the tube 2I and the casing I0. Adjacent, the lower end of the tube 22 is rigidly mounted a disc 26 having apertures 21 i'or a purpose to be pointed out hereinafter. This terminal I4 is made thimble-shaped with the outer surface 32 screw threaded to engage cooperating screw threads on the inner surface of the flange 20 of the screw cap I2. The upper end of the thimble-shaped portion -is provided with an outwardly extending flange 33 which cooperates with the gasket 34 and the upper surface of the cap I2 to provide a seal for the upper end of the casing I0. The inner surface of the thimble-shaped portion 3| is also provided with "screw threads to receive the screw-threaded clamping plug 35 which has an axially extending passage to receive the supporting shank I5 of the fusible element. This plug 35 is arranged to press downwardly upon theWedge-shaped member 36, also centrally bored to receive the shank I5, and to thereby effect a strong clamping action upon the shank. When the upper connection terminal is removed from its mounting in the end cap, an opening through the flanged portion 20 is provided through which the screw cap I8 of the movable terminal I1 can be unscrewed by means of a long screw driver. A new fusible element and its supporting shank may then be inserted through the opening in the cap I2 and the lower end of' the fusible element may beclamped to the terminal I1 by means of the screw cap I3. Terminal I4 is slipped over the supporting shank of the fusible element and is screwed into place as previously indicated. The projecting (md of the shank I5 is then pulled out to a sufficient extent to bring the shoulder 23 of the tube 22 into engagement with the lower end of the tube 2l whereupon the shank is clamped in place by means of the wedge-shaped member 33 and the screw plug 35.

When the element I6 fuses, the spring 28 fixed to the movable terminal I1 draws the terminal and also the tube 22 downwardly to the position shown in Fig. 2. It will be seenl that the two tubes 2I and 22 serve as an arc quenchy ing pressure resistant 'chamber which is extended as the arc is extended. Tube -22 has such length that it is -not complely 'withdrawn from case of alternating current, is hindered. Furthermore, during the downward drawing of the tube 22 under the influence of the spring 23, streams of the oil or other arc quenching liquid II are projected by means of 'the apertures 21 in the direction indicated by the arrows into proximity to the end of the terminal I1 and into the arc path sothat metal particles are driven away from the terminal and from the arc path.

A better quenching action is secured thereby and also fresh arcing is hindered.

Fig. 3 shows a modified construction in which the movable pressure tube 22 is not drawn out to the bottom of the casing I0 but is prevented in this construction from being completely withdrawn from the tube 2l by means of the projecting stop 31. Furthermore, in order to obtain a. better quenching action at quite high voltage, a projecting baille 38 is wound spirally upon the inner surface of the tube 22 in order to give the liquid discharged through the apertures 21 a screw-like motion.` In this manner the tearing away of the metal particles from the point of attachment 39 of the arc is made to take place to a greater degree than would be provided by the simple flow of the liquid upwardly through the tube 22. The projection 24, of which there may be several, provided on the inner surface of the tube 22 as shown in Fig. 1 is capable of .fulfilling substantially the same purpose as the screw-like baille shown in Fig. 3.

Fig. 4 illustrates a modification of the fuse constructions of Figs. 1-3, which modification is particularly adapted for employment in the practice of the invention of my divisional application, hereinbefore identified. In this last construction an inductive coil 40 is mounted in any suitable manner upon the casing I0 and concentrically with relation to the casing. This coil may be connected in an alternating current circuit as will be pointed out hereinafter. The lower end of the movable tube 22 is provided with a core member 4I of iron or other suitable magnetizable material so that when'the tube 22 is drawn downwardly under the influence of the spring 28 subsequent to rupture of the fusible element, the core-member is also drawn downwardly and into the magnetic field of the coil 40. This has the effect of reducing the reluctance of the magnetic path of the coil with a consequent increase in the inductance of the coil.

The action of the fuse device illustrated in Fig. 4'may be utilized to great advantage in the actuation of switching mechanism in the manner described in detail and claimed in my previously identified divisional application. In Fig. 5 is illustrated diagrammatically the manner in which such a fuse device may be employed as a protective device for a polyphase alternating current circuit. Three fuses 42, of the type illustrated in Fig. 4, are connected one in each of the phase conductors of the three phase circuit and each of the fuses has associated therewith an inductive coil 43 similar to that designated by the numeral 40 in Fig. 4. A source of potential 44 supplies current through conductors 45 and the inductive coils 43 to the coil 46 of relay 41, the con- 41 closed so that holding coil 48 is energized to maintain the circuit interrupter 49 closed. Upon the occurrence of a fault in any one` of the -phases of the three phase circuit, the corresponding fuse 42 operates and the core 4I thereof (shown in Fig. 4) is drawn downwardly into the' magnetic field of its associated coil 43 thus' increasing the inductive reactance of the circuit in which the coils 43 are connected and reducing f three phase circuit interrupting switch 49 under the influence of spring ill. In Fig. 5,the elements of the electric circuit` are shown in the state which they assume subsequent to operation of one of the fuses 42 so that the circuit interrupting switch is in open position and the whole circuit is deprived of current.

In Fig. 6 is illustrated diagrammatically a protective arrangement in which a fuse of the type illustrated in Fig. 4 is employed for effecting fthe sectionalizing of an electric circuit or more specically for the isolation of electrical converting apparatus, which may be either a rectier or an inverter, upon the occurrence of a fault therein. In Vthiscase ,the fuses 42 are connected in the phase conductors of the alternating current side of a conversion apparatus 5I and have associated therewiththe inductive coils 43 in a manner similar to that illustrated'in Fig. 5. The alternating current circuit interrupting switch 49 and the controlcircuit therefor incorporating the in'ductive coils 43 are also substantially the same as illustratedin 5. In addition, the direct current side of the conversion apparatus is provided with an interrupting switch 52 which is biased to open position b y means of a spring 53 and which is provided with an operating or holding coil 54 which is connected to relay" in parallel with the coil 48 of the interrupting device 49. Upon operation of any one of the fuses 42 due to a fault in its corresponding phase, the relay 41 drops'out in a manner similar to that described in connection with the arrangement of Fig. 5 and both the holdng coils 48 and 54 are deenergized so that the interrupting devices 49 and 52 respectively are operated to open position to thereby eiect isolation of the conversion apparatus from the remainder of the electric circuit.

What I claim as new and desire to secure by Letters Patent in the United States is:

1. An electric protective device comprising an enclosing casing, a' pairV of hollow tubes in tele- V.scoped relationship in the casing and providing a pressure resistant arc quenching chamber interiorly ofthe tubes, at least one of the tubes being longitudinally movable relative to the other, a pair of terminals associated respectively with said tubes andha-ving a fusible element connected therebetween so as normally to restrain the tubes in a relatively close coupled telescoped relationship, means operative upon rupture of said fusible element to eiect relative movement apart of said terminals and also longitudinal relative movement apart of said tubes so as to extend said chamber, and means for interposing arc quenching medium between said terminals, said tubes having such length relative to each .other that .they are not completely withdrawn associated respectively with said tubes and havfing a fusible element connected therebetween so as normally to restrain the tubes in a relatively close coupled telescoped relationship, means operative on rupture of said fusiblefelement to effect Y partial withdrawal of said one tube from telescoped relationship with said other tube so as to extend said chamber= liquid directing means associated with said one tube for directing a stream of said liquid between said terminals, and means operative to prevent-complete withdrawal "of said one tube from telescoped relationship with said other tube.

3. A protective device for an electric circuit, including in combination a hollow tubular casing having closed ends and abody of electric arc quenching liquid disposed therein, a pair of telescoped hollow tubular members disposed in said casing with one of said members flxedly mounted and the other of said members axially slidable withrelavtion to the fixed member, fuse contacts mounted one in each of said tubular members, a fuse element extending between said contacts and operative normally to maintain said members in telescoped relationship, spring means in said casing operative upon fusion of said element to draw said slidable member at least partially out of said iixed member, means providing apertures in said slidable member for directing streams of said arc' quenching liquid into proximity with the contact in the slidable member upon movement of the slidable memberdue to fusion of said fuse element, and baille means disposed on the inner surface of the slidable member for more eiectively directing said streams of liquid into the arc path between said contacts.

4: A protective device for an electric ycircuit, including in combination a hollow tubular casing having closed ends and a body of electric arc Y quenching liquid disposed therein, a pair oi telescoped hollow tubular members disposed in said casing with one of said members flxedly mounted and the other of said members axially slidable with relation to the flxedmembers, contacts mounted one in each of said members, fusible means extending between said contacts and operative normally to maintain said members in telescoped relationship, means in'said casing operative upon rupture of said fusible means to draw said slidable member at least partially out of said fixed member, means providing apertures adjacent the outer end of said slidable member for directing streams of said arc quenching liquid into the space between said contacts upon movement of the slidable member due to rupture of said fusible means, and means providing an inwardly projecting bale wound spirally on the inner surface of the slidable member for creating a screw-like flow of the liquid discharged through said apertures.

5. A protective device for an electric circuit including in combinationa xedly mounted hollow tubular casing having one end open, a second hollow tubular casing telescoped within said first casing and axially slidable with respect thereto, a fusible element having one end aiiixed in each of said casings and normally operative to maintain said second casing telescoped within said rst casing, said casings cooperating to provide a pressure resistant arc quenching chamber within the interior thereof, means for withdrawing said second casing from said rst casing upon rupture of said fusible element, and stop means mounted for preventing complete withdrawal of said second casing from said first casing in order that an arc formed upon the rupture of said fusible element will be quenched solely within the pressure resistant chamber formed by said c asings.

6. A protective device for an electric circuit including in combination a hollow tubular casing of insulating material having one end open, a second tubular casing of insulating material disposed substantially coaxially of and telescoped within said ilrst casing and axially slidable with respect to the iirst casing, a pair of connection terminals mounted one in each'of said casings, a 'fusible element extending between said terminals and normally operative to maintain said second casing teiescoped within said first casing, said lcasings cooperating to provide a pressure reva pair of hollow tubes telescoped one within the other and relatively movable, an elongated rodlike terminal element supported rigidly with respect to the outer of said tubes and extending a substantial distance into and substantially along the axis of said tubes, a terminal element carried by th'e inner one ofsaid tubes, said terminal elements being adapted to support a fusible element connected therebetween for maintaining said tubes in telescoped relationship, means ar- 8. In a protective device for an electric cir-V cuit, a hollow tubular casing, a hollow tube rigidly supported substantially coaxially within said casing, a second hollow tube movably telescoped in one end of said first tube, a pair of terminals carried one by each of said tubes and adapted to support a fusible element connected therebetween for maintaining the tubes in telescoped relationship, means arranged to draw said tubes apart to increase 'the distance between said terminals upon rupture of a fusibleelement connected between the terminals, and a radially extending shoulder carried by the outer end oi said second tube and arranged to abut against the said one end of said ilrst tube when the tubes are in telescoped relationship, said shoulder also extending into relatively close proximity with the wa11\ of said tubular casing for slidable cooperation therewith to insure substantially pure axial movement of said second tube in said casing.

GUs'rnv w. MLLER. 

